Voting 5 to 4, the justices found, in a two-paragraph opinion, that the Supreme Court's Citizens United ruling applied to a 100-year-old Montana anticorruption law barring corporate money in elections.

Washington — In a reaffirmation of its controversial Citizens United decision on campaign finances, the US Supreme Court on Monday struck down as unconstitutional a 100-year old Montana law that banned corporations from spending money to influence state elections.

The high court voted 5 to 4 to summarily reverse a December 2011 decision by the Montana Supreme Court upholding the state’s Corrupt Practices Act of 1912.

The 1912 ban on corporate money in elections was passed to prevent a return of the widespread corruption of the “Copper Kings,” when wealthy and powerful mining interests in Montana routinely bought judges, controlled newspapers, and bribed lawmakers.

“The question presented in this case is whether the holding of Citizens United applies to the Montana state law,” the unsigned opinion said. “There can be no serious doubt that it does.”

In its 2010 decision, Citizens United v. Federal Election Commission, the high court ruled that a federal ban on independent expenditures prior to an election violated the First Amendment rights of corporations and labor unions to engage in political speech free of government censorship.

“Political speech does not lose its First Amendment protection simply because its source is a corporation,” the court held.

The Montana high court ruled that the Citizens United decision did not apply in their state because Montana had a long history of election-related corruption that justified restrictions on corporate spending even a century later.

Justice Stephen Breyer said in a dissent that he would have voted to hear the Montana case and use the case as a vehicle to reconsider the underlying decision in Citizens United, but it was clear there were not enough votes to do that. Three other justices joined Breyer’s dissent; Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan.

“This court’s legal conclusions should not bar the Montana Supreme Court’s finding, made on the record before it, that independent expenditures by corporations did in fact lead to corruption or the appearance of corruption in Montana,” Breyer said.

“Given the history and political landscape in Montana, that court concluded that the state had a compelling interest in limiting independent expenditures by corporations,” he wrote.

“Montana’s experience, like considerable experience elsewhere since the court’s decision in Citizens United, casts grave doubt on the court’s supposition that independent expenditures do not corrupt or appear to do so.”

The high court reversal brought praise from free speech advocates and disappointment from supporters of campaign finance reform efforts.

“The Supreme Court is broken,” said Russ Feingold, a former US senator from Wisconsin Senator and a champion of campaign finance reform. “The Supreme Court had a perfect chance today to clean up the corrupt mess created by their lawless Citizens United decision. Instead, they just shrugged.”

He said a review of federal records shows that of the $96 million contributed to the eight Republican Super PACs, less than14 percent came from corporations and less than 1 percent from public companies. “Clearly, the much predicted corporate tsunami that critics of Citizens United warned about simply did not occur,” he said in a statement.

Montana Sen. Jon Tester predicted the ruling would “open the gates to even more out-of-state money from secretive special interests.”

“This decision rolls back 100 years of transparency in Montana, returning us to an era when millionaires and billionaires bought elections for themselves,” he said. “That’s not free speech; it’s corruption.”

Although states and the federal government are free to restrict the amount of money corporations may contribute to a political candidate, they may not limit the amount of money a corporate spends on its own – independent of any candidate – to express political ideas in advertisements or other forms of political expression.

That was the central holding of Citizens United.

Campaign finance reform advocates say the decision opened the floodgates to corporate money and influence in elections, threatening to distort and corrupt the democratic process.

As evidence, they point to the increasing political clout of independent election spending groups and so-called super PACs during the current election.

Free speech advocates, who support the Citizens United decision, say corporations – like individuals – are entitled to speak on matters of public concern without facing prior approval or censorship by the government.

At issue in the Montana case was whether the state supreme court correctly applied the Citizens United decision in a lawsuit challenging Montana’s ban on independent political expenditures by corporations.

Under the Montana statute, corporations were only allowed to make political expenditures with funds raised and distributed through political action committees or PACs.

Following the Citizens United decision in 2010, three firms sued the state, charging the corporate ban on political spending was unconstitutional.

A state judge agreed, but the Montana Supreme Court reversed.

The state high court vote was 5 to 2. “Unlike Citizens United, this case concerns Montana law, Montana elections and it arises from Montana history,” the court said.

The Montana high court drew a distinction between the complex federal campaign finance laws struck down in Citizens United and the Montana statute. The state court said Montana’s law was easy to follow and allowed corporate officers to make individual contributions and to channel political spending through PACs.

The state high court also emphasized Montana’s extensive history of corruption as a compelling reason justifying the continued necessity of the 1912 state law.

“The question then is when in the last 99 years did Montana lose the power or interest sufficient to support the statute, if it ever did,” the Montana justices asked.

It changed, according to five members of the US Supreme Court, in January 2010 when the Citizens United decision was announced and became the law of the land – including in Montana.

Since the US Constitution applies to both the federal and state governments, state courts are required to uphold Supreme Court decisions even if a majority of state supreme court judges disagree with the underlying ruling.

When state courts fail to uphold a US Supreme Court precedent, the high court sometimes takes the unusual step of summarily reversing the state court. A summary reversal means that the Supreme Court decides the issue without the benefit of full briefing and oral argument. In effect, the court is saying that the Montana Supreme Court’s mistake was so clear and so blatant that further consideration is unnecessary.